Wireless radio communication systems are well known in the art. Such systems include cellular telephone systems, trunked dispatch systems, and mobile data systems. Early radio systems generally offered a single service. However, some current systems now offer multiple services, such as telephony and trunked dispatch services, on a common set of radio communication resources. One such system is described in U.S. Pat. No. 5,548,631 (hereinafter the '631 patent).
Radio systems which initially offered multiple services provided such services by using a single system controller that coordinated the usage of all radio communication resources and the call processing of all calls. Such coordination has been centralized for all sites, as in the "SmartNet" system that is commercially available from Motorola, Inc. of Schaumburg, Ill., and distributed with one controller for the radio communication resources for each site and another central controller to maintain control over all call processing, as in systems that implement the Global System for Mobile Communications (GSM) standard. Central coordination of call processing leads to an increased complexity of the central controller, in one part due to the different nature of the calls of each service and in another part due to the differing market maturity of each service.
As an alternative approach to distributed control, the '631 patent describes a technique in which the call control is implemented separately in various controllers, or servers, with little concern over the interaction between services. As described in the patent, the radio communication resources are maintained by a control process at the site that arbitrates between conflicting requests from the various servers.
However, another interaction between services is of concern in the system described in the '631 patent because the system described in the patent includes a plurality of base sites. In a radio communication system that includes a plurality of base sites, there must be communication links between the centralized equipment and all the sites that are not collocated with the centralized equipment.
The communication links are generally provided by a public utility company (e.g., telephone company) and, therefore, generally involve a recurring cost. Thus, it is advantageous to minimize the needed bandwidth between the centralized equipment and each of the remote sites, thereby reducing the bandwidth required of each communication link. However, the bandwidth required for each of the services is not known apriori, except that it is limited by the available radio frequency (RF) bandwidth provided by the installed equipment at each of the base sites. Therefore, at any point in time, each service is independently limited by the available RF bandwidth and the aggregate bandwidth of the services is also limited to that same RF bandwidth. In such a situation, one service could use most or all of the RF bandwidth at one time and another service could use most or all of the RF bandwidth at another time.
Since the aggregate bandwidth of the services is limited, an effective method of providing the switching and transportation needs between the servers and the base sites is to use a common packet switching network and a shared communication link between each base site and the centralized communication equipment. However, the characteristics and attributes of each of the services may be such that when applied to a shared communication link, they conflict in such a way as to render one or more of the services unacceptable.
For example, audio delay in a telephony or trunked dispatch voice communication system conflicts with packet data systems in the following way. Audio delay in telephony and trunked dispatch voice communication systems is very critical because users find voice services difficult to use when audio delay is above a couple hundred milliseconds (and only a small portion of this delay would be attributable to the packet switch and transport). On the other hand, packet data systems often transport very large packets (on the order of thousands of bytes of information). Assuming a shared link of 64 kilobits per second (typically referred to within the telephony environment as a single DSO), a data packet with 8,000 bytes of information (64 kilobits) would take a full second to transport on the shared link and would, therefore, delay any voice packets that happened to arrive after the start of the data packet transmission by up to one second. Such a delay would render the voice packets so late as to be unusable and, therefore, severely impair the voice service.
Another approach to adding a new service, such as data, to an existing service, such as telephony, in a multi-site communication system is provide separate links and switches for each service. Such is the approach used to implement cellular digital packet data (CDPD) in existing Advanced Mobile Phone Service (AMPS) systems. However, such an approach is costly due to the requirement of having multiple switches and communication links.
Therefore, a need exists for a multi-service communication system and method for providing information packets from a multiple server packet switching network to a base site in such a communication system that minimizes the bandwidth needed between the packet switching network and the base site and provides an acceptable transport quality to each of the services.